This application is based on Japanese Patent Application No. 11-236278 (1999) filed Aug. 24, 1999, the contents of which are incorporated hereinto by reference.
1. Field of the Invention
The present invention relates to a serial type printing apparatus (also referred to as a xe2x80x9cprinterxe2x80x9d) and a printing method using this printing apparatus. More specifically, the present invention relates to a printing apparatus and a printing method which uses a multi-pass printing mode in which a printing head scans a same area of a printing medium a plurality of times to complete the printing.
In addition to general printing apparatus, the present invention can be applied to copying machines, facsimiles with a communication system and word processors with a printing unit and also to industrial printing apparatus combined with a variety of processing devices.
2. Description of the Related Art
As information devices such as computers become more widespread, the printing apparatus such as printers are also finding an increasing range of applications. Of these, a so-called serial type printing apparatus, in which the printing head being arranged a plurality of printing elements is scanned over the printing medium to perform the printing, is coming into rapidly increasing use because of its compact size and low cost.
Some such serial type printing apparatus have a multi-pass printing mode that prints an image with a higher quality than a normal mode provides. The printing in this multi-pass printing mode is carried out as follows. The printing head is scanned over the printing medium in a direction perpendicular to the arrangement direction of the printing elements and, after this one scan, the paper is fed in the arrangement direction of the printing element by a distance shorter than the height of the printing head. This sequence of operations is repeated. The printing head scans the same printing area of the printing medium a plurality of times to complete the printing. Suppose, for example, the height of the printing head is H and the distance that the paper is fed once is x, the printing head completes the printing on the same area of the printing medium by performing the scan operation (H/x) times.
In such a multi-pass printing mode, the printing elements in the printing head are grouped into several blocks in the order of arrangement, each having a length equal to the distance x of once paper feeding. In a first scan the image data of a predetermined area on the printing medium are printed by a first block of the printing elements. In a second scan after the paper has been fed a distance of x, the same image data are printed by a second block of the printing elements. Hence, in this multi-pass printing mode, many printing apparatus adopt a construction in which the image data read out from an image data storage means can be rotated or shifted one block length x at a time to any desired location of the printing head for printing, without moving the image data itself which are stored in the image data storage means. The term xe2x80x9crotatexe2x80x9d means shifting data a predetermined unit at a time. Because the same area of the printing medium is scanned by the printing head a plurality of times to complete an image, it is often the case that data thinning processing is performed to print the image data with a plurality of complementary scans by the printing head. In this way, a means is provided to perform a predetermined thinning operation on the rotated or shifted image data.
If the printing head performs printing in an area covering or beyond the rear end of the printing medium, ink may adhere to other than the printing medium, for example, platen. To solve this problem, as disclosed in Japanese Patent Application Laid-Open No. 7-47740 (1995), the printing medium is not fed beyond the printable area when the printing is performed at the rear end. Instead, the data to be printed is shifted toward the upstream side with respect to the printing medium feed direction so that the printing can perform to the full extent of the scannable area.
When the multi-pass printing is performed at the rear end part of the printing medium, however, it is necessary to simultaneously perform a data rotation for the multi-pass printing and a data rotation for correction during the rear end printing. In conventional apparatus there is only one means for rotating or shifting the image data, so the amount of rotation for the one rotation means must be determined by considering both a rotation amount for the multi-pass printing and a rotation amount for the rear end correction.
When the rear end of the printing medium is to be printed by the multi-pass printing, the data to be printed needs to be corrected by shifting it toward the upstream side of the printing medium while at the same time thinning the data for each pass. The conventional apparatus, however, is provided with a data thinning means that performs a data thinning operation on the rotated data output from a rotating means. Hence, when the rear end portion of the printing medium is to be printed by the multi-pass printing, not only the rotation of the image data by one rotating means must be controlled, but the data thinning pattern itself must be separately shifted on the buffer which stores the data thinning pattern, in order to correctly complete the multi-pass printing.
The object of the present invention is to provide a printing apparatus and a printing method that perform printing within a printable area and complete the multi-pass printing correctly even when the rear part of the printing medium is printed by the multi-pass printing.
In a first aspect of the present invention, there is provided a printing apparatus for forming an image on an entire surface of a printing medium by scanning a printing head being arranged a plurality of printing elements over the printing medium a plurality of times in a direction different from that in which the printing elements are arranged and by moving, between the plurality of scans, the printing medium relative to the printing head in a direction different from that in which the printing head is scanned, the printing apparatus comprising:
a printing medium feeding unit for moving the printing medium a predetermined feed distance relative to the printing head;
a data storing unit for storing image data for one scan of the printing head;
a first rotating unit for reading out the image data stored in the data storing unit and rotating the image data a predetermined number of times, one block of data at a time, the one block representing a predetermined amount of data;
a thinning unit for thinning the image data output from the first rotating unit with a predetermined pattern; and
a second rotating unit for reading out the image data thinned by the thinning unit and rotating the image data a predetermined number of times, one block of data at a time, the one block representing a predetermined amount of data.
In a second aspect of the present invention, there is provided a printing method using a printing apparatus, wherein the printing apparatus forms an image on an entire surface of a printing medium by scanning a printing head being arranged a plurality of printing elements over the printing medium a plurality of times in a direction different from that in which the printing elements are arranged and by moving, between the plurality of scans, the printing medium relative to the printing head in a direction different from that in which the printing head is scanned, the printing method comprising:
a printing medium feeding step for moving the printing medium a predetermined feed distance relative to the printing head;
a data storing step for storing image data for one scan of the printing head;
a first rotating step for reading out the image data stored in the data storing step and rotating the image data a predetermined number of times, one block of data at a time, the one block representing a predetermined amount of data;
a thinning step for thinning the image data output from the first rotating step with a predetermined pattern; and
a second rotating step for reading out the image data thinned in the thinning step and rotating the image data a predetermined number of times, one block of data at a time, the one block representing a predetermined amount of data.
With the above construction, of the two rotating means, one is used as the data rotating means for the multi-pass printing and the other as the data rotating means for the printing correction at the rear end part of the printing medium. So, this allows these processing to be performed by separate algorithms. And the amounts of rotation can be calculated separately.
The above and other objects, effects, features and advantages of the present invention will become more apparent from the following description of embodiments thereof taken in conjunction with the accompanying drawings.